"APL's dual combustion ramjet is yet another way to obtain hypersonic
speeds. In this powerplant, supersonic air ingested through one inlet
is slowed to subsonic speeds, mixed with a conventional hydrocarbon
fuel in a fuel-rich environment and ignited, as in a ramjet. To break
through the ramjet's operating speed limitations, though, the expanding
combustion products are then mixed with supersonic air entering through
a second inlet and are more completely burned in a supersonic
combustor.

Interesting. Could this be done in three or more stages?

.. . .

Quote:

I shall argue that the method of not slowing the incoming air at all
but accelerating the fuel up to the relative air speed will result in a
marked improvement in fuel efficiency.

Ever look at the P-V diagrams for an internal combustion engine without
compression?

"APL's dual combustion ramjet is yet another way to
obtain hypersonic speeds. In this powerplant,
supersonic air ingested through one inlet is slowed
to subsonic speeds, mixed with a conventional
hydrocarbon fuel in a fuel-rich environment and ignited,
as in a ramjet. To break through the ramjet's operating
speed limitations, though, the expanding combustion
products are then mixed with supersonic air entering
through a second inlet and are more completely
burned in a supersonic combustor.

Interesting. Could this be done in three or more stages?

What are we going to do when:
- the water vapor at high altitiude breaks the "oxides of
nitrogen" cycle of ozone production, and
- these engines consume the very oxygen that ozone is made from?

(I.) In this thread I argued for using the boundary layer air at zero
relative velocity to the craft to eliminate the problem of the ram
drag created by ingesting and slowing down the surrounding air for
combustion:

Another possibility would be to accelerate the fuel up to the same
velocity of the craft then eject this into the air flow. Call it
Accelerated Fuel Combustion (AFC). Then you would not have to slow down
the air inflow at all for combustion. The problem then would be to be
able to accelerate the fuel up to the maximum velocity of the craft to
reach orbit, about 7.5 to 8 km/sec.
DARPA and Johns Hopkins' Applied Physics Laboratory are already
investigating a partial version of this idea at lower velocities:

New Powerplant Key To Missile Demonstrator
By Stanley W. Kandebo/Aviation Week & Space Technology
September 3, 2002
"APL's dual combustion ramjet is yet another way to obtain hypersonic
speeds. In this powerplant, supersonic air ingested through one inlet
is slowed to subsonic speeds, mixed with a conventional hydrocarbon
fuel in a fuel-rich environment and ignited, as in a ramjet. To break
through the ramjet's operating speed limitations, though, the expanding
combustion products are then mixed with supersonic air entering through
a second inlet and are more completely burned in a supersonic
combustor. According to APL researchers, the DCR has an operating
threshold of about Mach 3, and a maximum operating speed of about Mach
6.5."
http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?view=story&id=news/mdcrj0903.xml

Sorry, but the real "innovation" here is doing away with the need to use
fuel cooled combustor panels, while at the same time raising the
temperature of the liquid JP fuel and partially cracking it to greatly
speed up kinetic rates.

In your "concept" what is the residence time of the fuel/air mixture in the
combustor compared to the reaction rates? This is all ready an issue which
must be dealt with in the design of moderate Mach number scramjets.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
http://edwardgruf.com/Digital_Photography/General/index.html

Sorry, but the real "innovation" here is doing away with the need to use
fuel cooled combustor panels, while at the same time raising the
temperature of the liquid JP fuel and partially cracking it to greatly
speed up kinetic rates.

If the hydrocarbon fuel was only partially burned in several stages
maybe liquid H2 cooling could be reduced or eliminated altogether.

Sorry, but the real "innovation" here is doing away with the need to use
fuel cooled combustor panels, while at the same time raising the
temperature of the liquid JP fuel and partially cracking it to greatly
speed up kinetic rates.

If the hydrocarbon fuel was only partially burned in several stages
maybe liquid H2 cooling could be reduced or eliminated altogether.

You're not getting the full picture. There are two classes of scramjet
powered vehicles. There is a lower Mach number liquid fueled class, say
Mach 8 and below. This is where the cooling capacity of a liquid JP fuel
may be enough to cool hot structure in both the vehicle and in the engine
making use of the high temperature endothermic fuel properties. However,
there is a limit on max fuel temperature due to coking and a limit on max
hot side metal temp due to the limits in cooling provided by the liquid
fuels. In fact the fuels tend to be supercritical in nature in these
systems as it is. The liquids are preferred where the system closes ( fuel
needed for cooling isn't much more than fuel needed for combustion) due to
the higher volumetric efficiency afforded to vehicles using liquid fuels.

At higher Mach much more heat capacity is needed, so these vehicles use
LH2. You also need faster kinetics as the residence time in the combustor
is shorter. H2 has much faster kinetics. It also has products, H2O which
are harder to dissociate at the higher combustor exit temps.

You don't see vehicles which use both as from a system standpoint you don't
win at least at this point of development. Maybe in the future when 3rd
fluid systems using an intermediate fluid or the cooling circuit are looked
at this may change. But it is past the SOA of today.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
http://edwardgruf.com/Digital_Photography/General/index.html

Well, what if you dispense with slowing the air down altogether? If
you ejected the fuel behind the vehicle - perhaps using electrostatics,
or some sort of detonation process - so that the speed of the ejected
fuel relative to the air was below that needed to sustain combustion,
and then detonated the air/fuel mixture outside the vehicle in a well
defined region - and well defined shape - using a laser or particle
beam - and rode the resulting shaped shock wave?

Bret Cahill wrote:

Quote:

First, you have to accelerate the fuel up to the velocity of the
craft which can be up

to 8 km/sec to reach orbit.

If you are planning on using a nozzle that will require a pressure of
millions of psi.

If you ejected the fuel behind the vehicle - perhaps using electrostatics,
or some sort of detonation process - so that the speed of the ejected
fuel relative to the air was below that needed to sustain combustion,

What the heck are you thinking about here? What actual physical processes
are you envisioning?

Quote:

and then detonated the air/fuel mixture outside the vehicle in a well
defined region - and well defined shape - using a laser or particle
beam - and rode the resulting shaped shock wave?

Again just how have you mixed the air and the fuel ? Without mixing you
have no combustible or detonable mixture. You just can squirt fuel out the
back and burn/detonate it.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)

Ejecting the fuel at a speed that brings its relative velocity down to
a reasonable speed relative to the movement of the air.

Quote:

If you ejected the fuel behind the vehicle - perhaps using electrostatics,
or some sort of detonation process - so that the speed of the ejected
fuel relative to the air was below that needed to sustain combustion,

What the heck are you thinking about here? What actual physical processes
are you envisioning?

Detonating a fuel air mixture external to the craft as in a fuel-air
explosive and somehow making use of a portion of the shockwave that
results to propel the craft - and if you're lucky, using a portion of
the shockwave's energy to eject your next round of fuel.

Quote:

and then detonated the air/fuel mixture outside the vehicle in a well
defined region - and well defined shape - using a laser or particle
beam - and rode the resulting shaped shock wave?

Again just how have you mixed the air and the fuel ?

Explosively

Quote:

Without mixing you
have no combustible or detonable mixture.

In an air-fuel explosive you have two explosions. One to detonate the
fuel and spread it into a cloud. The second, to detonate the cloud.

You could do that here. You could eject a plastic bottle of fuel from
a gun, with one explosion bringing it to rest in the air behind the
aircraft, detonate the bottle with a second explosion spreading the
fuel into an air-fuel mixture, then detonating the air-fuel mixture to
create a shock wave. The shock wave propels the vehicle.

Quote:

You just can squirt fuel out the
back and burn/detonate it.
--

Well, you have to be careful with the details, but if you can use a
air-fuel bomb to smash a tank on the ground, it seems to me you might
have a shot in creating an air-fuel mixture behind a hypersonic
aircraft that has a shot at propelling the aircraft.

Ejecting the fuel at a speed that brings its relative velocity down to
a reasonable speed relative to the movement of the air.

High philooting words at best, how about some specifics?

Quote:

Again just how have you mixed the air and the fuel ?

Explosive
Baloney. You haven't said how you actually intend to mix the air with the

fuel. How about giving us some mixing correlation you have in mind of
trying to implement?

Quote:

Well, you have to be careful with the details, but if you can use a
air-fuel bomb to smash a tank on the ground, it seems to me you might
have a shot in creating an air-fuel mixture behind a hypersonic
aircraft that has a shot at propelling the aircraft.

Conjecture. That's mixing at zero velocity. You can't just wave your hands
and extrapolate that to supersonic shear layer mixing. The airflow has
orders of magnitude more kinetic energy in it. The laws of physics don't
work that way. Let's see the mathematics behind your concept.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)

have no combustible or detonable mixture. You just
CAN"T
squirt fuel out theback and burn/detonate it.

--
Ed Ruf (Usenet2@EdwardG.Ruf.com)

I agree. But you can eject fuel in a bottle, with one explosion,
spread fuel with a second explosion, into an air-fuel explosive
mixture, and detonate it with a third explosion. You can then ride the
resulting shock wave.

This is the crudest way to achieve this result. A cooler way would be
to electrostatically eject the fuel from a large number of small
nozzles (think inkjet printer type surface facing rearward) and then
detonate the resulting cloud with some sort of electrostatic discharge.

Of course, when I say eject this out of the back of the aircraft,
that's one approach without tubes or channels of any sort. Another
approach would be to create some sort of tube or channel, that didn't
even try to slow the ram air down - a tube or channel that diverged
would actually speed the flow in the channel or tube up when operating
at supersonic speed.

Anyway, eject the propellant into the stream with a speed that brought
the propellant to a low speed relative to the moving air, and then,
spread it, and detonate it when it was at the right air/fuel mix, and
ride the resulting shock wave.

Careful design might even use the high stagnation temp to create a
detonation wave and hold it by controlling channel or tube width with
length. Likely such a device would have to change shape with speed.
But a channel equipped with flaps that ejected droplets from behind
them, might be workable.

For gasoline vapor, the explosive range is from 1.3 to 6.0% vapor to
air, and for methane this range is 5 to 15%. Many parameters contribute
to the potential shock from a vapor cloud explosion, including the mass
and type of material released, the strength of ignition source, the
nature of the release event (e.g., turbulent jet release), and
turbulence induced in the cloud (e.g., from ambient obstructions).

Based on the known properties of flammable substances and explosives,
it is possible to use conservative assumptions and calculate the
maximum distance at which an overpressure or heat effect of concern can
be detected. Distances for potential impacts could be derived using the
following calculation method [described in Flammable Gases and Liquids
and Their Hazards]:

D = C x (nE)^1/3

where D is the distance in meters to a 1 psi overpressure; C is a
constant for damages associated with 1 psi overpressures or 0.15, n is
a yield factor of the vapor cloud explosion derived from the mechanical
yield of the combustion and is assumed to be 10 percent (or 0.1) and E
is the energy content of the explosive part of the cloud in Joules. E
can be calculated from the mass of substance in kilograms times the
heat of combustion (hc) in Joules per kilogram as follows:

E = mass x hc

Combining these two equations gives:

D = 0.15 x (0.1 x mass x hc)^1/3

Vapor cloud explosion modeling historically has been subject to large
uncertainties resulting from inadequate understanding of effects.
According to current single-degree of freedom models, blast
damage/injury can be represented by Pressure-Impulse (P-I) diagrams,
which include the effects of overpressure, dynamic pressure, impulse,
and pulse duration. The peak overpressure and duration are used to
calculate the impulse from shock waves.

Aviation fuel has 43 MJ/kg at a reasonable altitude air has a density
of about 0.4 kg/m3 (1/3 sea level density) and at 2% density - the
vapor would possess 0.008 kg/m3 - and would release about 344 kJ per
m3.

This of course is all stationary - and at Mach 5 for example, at 10,000
m ( a little over 30,000 ft) that speed is 1,500 m/sec. So, each
SQUARE meter sees 1,500 cubic meters of air flow through it every
second ON AVERAGE. So, that's a power of 516 Megawatts per square
meter and a fuel consumption of 12 kg per second. Kerosene masses 0.81
kg/Liter so this is equal to 9.72 liters per second per square meter.

Now, the power needed to eject 12 kg per second at a speed of 1,500
m/sec is;

If the fuel is stationary in the air, and evenly spread by a spreading
explosion or equivalent, the shockwave radiates in all directions far
from the explosion - at the speed of sound. A series of explosions
like this would create a resulting shockwave whose angle relative to
the flow would have an angle equal to;

angle = arc-cos(1/M)

and since in this case we said M was 5 then the angle is 78.46 degrees.

So, if a ring of propellant were detonated behind an aircraft body with
a conical rear surface with an opening angle of 22 degrees - part of
the shock made by the exploding ring of fuel air would compress the
back of the aircraft body propelling it forward - the same way pressing
your fingers together on the back of a slippery pumpkin seed propels it
forward at many times the closing velocity of your fingers.

In its simplest implementation you have a bottle of fuel equipped with
a couple of fireworks. Say a 2 liter bottle of kerosene. That masses
about 1.62 kg, and contains about 70 MJ of energy. It will detonate if
brought to between 2% and 6% of the air mass and detonated.

Now air masses around 1.2 kg per m3 near the surface and drops to about
0.4 kg per m3 at 10,000 m altitude - 30,000 ft- so you could run a
detonation if you had a spreader explosion that spread the 2 liter
bottle across a volume of say 40 cubic meters of space. That's a
sphere around 4 meters across. Once you've got your air fuel spread
across this volume, you then have a second firework that detonates it.

So, the sequence is rather simple.

You throw a bottle of kerosene out the back of a fast moving aircraft,
so that it comes to rest relative to the air. You then detonate a
spreading explosion that spreads it to the appropriate air-fuel mix
ratios. Then you detonate a second explosion that detonates the air
fuel mix. If you did things right, the resulting shockwave will impact
some sort of propulsive surface that will produce thrust from the
explosion.

Quote:

Again just how have you mixed the air and the fuel ?

Explosive
Baloney.

Why do you say that? Fireworks have routinely been used to create
air-fuel mixes in thermobaric weapons. Absolutely no reason they
cannot be used here.

Quote:

You haven't said how you actually intend to mix the air with the
fuel.

Well the air surrounds the aircraft, you toss a bottle of fuel out the
aircraft in a way that brings it to rest in that airstream, you then
detonate the bottle to spread it to the right air-fuel ratio, and then
you detonate the cloud of air fuel to create a shockwave - you then
catch the shock wave to provide propulsive force.

Quote:

How about giving us some mixing correlation you have in mind of
trying to implement?

Sure. Kerosene explodes at air/fuel mass ratios from 2% to 6% - so a
two liter bottle would need to be spread across a sphere about 4 meters
in diameter - and then detonated with a second explosion. Think of a
4th of July firework.

Of course we don't need to use two liter bottles. We could use vitamin
capsule sized bottles or five gallon gas tank bottles - or anything in
between.

Since this is a half-baked notion, there's no reason we couldn't eject
droplets at a speed that brought them to rest in the airstream with a
large number of ejectors, and then detonated them at the right spot
near the aircraft's surface with a spark or something.

Quote:

Well, you have to be careful with the details, but if you can use a
air-fuel bomb to smash a tank on the ground, it seems to me you might
have a shot in creating an air-fuel mixture behind a hypersonic
aircraft that has a shot at propelling the aircraft.

Conjecture.

That a shock wave can push something? A pretty reasonable conjecture I
must say.

Quote:

That's mixing at zero velocity.

That's the whole point. If you can't figure out how to do something
one way, do it a way you CAN figure out. Bringing the fuel to rest
relative to the air does that.

Quote:

You can't just wave your hands
and extrapolate that to supersonic shear layer mixing.

You're doing that not me. I'm doing something very simple. Eject the
fuel so that it is at rest relative to the air moving around the
vehicle. Then, spread it if need be, and detonate it.

Quote:

The airflow has
orders of magnitude more kinetic energy in it.

Now you're just spouting words. You missed the essential feature of
what I've described.

Quote:

The laws of physics don't
work that way.

Not the way YOU describe - no. Because you missed a rather simple
point. The fuel and air are sitting still while the aircraft is
zipping by. lol.

Quote:

Let's see the mathematics behind your concept.

What mathematics would you need exactly? Its really rather simple.
You eject the fuel so that it is stationary in the air, you spread it
if need be to get to the right air/fuel ratio, and then you detonate
the mix - creating a shock wave. The shock wave moves at sound speed,
so that means a series of these spherical shock waves will have a Mach
Cone whose angle is equal to the ACOS(1/M) - if you insist on math.
lol.

A tapering tail cone would pick up the shock cone of a successive
detonation of rings of fuel around the aircraft in this way, and
produce thrust. Just as swept wings reduce the effective velocity
across the chord, so too does a tapered propulsive surface reduce the
effective velocity of the aircraft so that it can interact efficiently
with the shockwave. Think of squeezing a pumpkin seed between your
fingers. The seed's speed when it exits your grasp, is several times
the closing speed between your finger and thumb! lol.